In addition to supporting a vehicle and maintaining wheel alignment, a vehicle suspension directs and distributes the resultant reaction forces from vehicles' braking system during braking. The simpler suspensions redirect brake reaction forces into the vehicle chassis using the vehicle body's normal weight to oppose the generated braking reaction forces.
It is known that such suspensions tend to bounce during skid control stops when the vehicle is empty or lightly loaded. These suspensions are highly susceptible to interacting together with skid control systems in such a way that bounce is sustained for the duration of the skid control stop. Stopping distances increase (due to decreased normal force available during a bounce) and susceptibility of vehicle and cargo to damage is increased.
As observed in films documenting bounce, several modes of suspension-skid control-wheel system behavior were evident in a tandem axle trailer:
A. With the first application of vehicles's brakes, all four wheels decelerate, but not necessarily to lock, and PA0 B. the skid control system responds by releasing air from brake chambers, allowing wheels to recover. PA0 C. Upon recovery of wheels to body velocity, the skid control system allows brakes to be reapplied, but all wheels this time seem to decelerate simultaneously to lock. PA0 D. Just as the wheels of both axles lock, the trailer container moves upward, and in the extreme case, takes the bogie and its wheels with it off the ground. Air again is exhausted from brake chamber, releasing brakes due to lock, and PA0 E. when the wheels reach the ground again on impact, skid control allows brakes to be reapplied immediately. This again lifts the container and trailer bogie, repeating step c, and in this way bounce is sustained for duration of the stop.
In addition, such suspensions also contribute to synchronous behavior during skid control cycling. Decreased traction, usually on the front axle, due to interaxle load shift while braking causes momentary loss of front tandem axle traction. This loss of traction causes rapid deceleration of front wheels in such a way that wheels usually snap to a lock, generating a force impulse that has to be absorbed by the vehicle body via suspension. With the upward motion of the vehicle body, these forces impart simultaneous decreased normal forces to the rear tandem causing loss of rear road traction, thus synchronizing the rear wheels with the fronts during wheel deceleration. This behavior aggravates bounce by synchronizing all the peak forces developed in front and rear tandem braking system.